1. Field of the Invention
This invention relates to a process for the selective removal of metal ions from an aqueous solution using a water-soluble polymeric chelant. The metal ion is chelated by the pendant chelating groups and then treated by separation means, such as dialysis or ultrafiltration, to remove water. The metal ion is then released from the chelate, generally using a dilute aqueous mineral acid, and separated. The chelant is then recycled and reused.
2. Description of the Relevant Art
A number of approaches have been reported to remove metal ions from aqueous solution.
K. S. Choi et al. in Pollimo, Vol. 5, No. 4, pp. 266-277 (1981) [See Chemical Abstracts, Vol. 96(2) 7417g] disclose a polymeric chelate for removing organic substances and heavy metallic ions from a water solution. A three-dimensional network structure is obtained by the reaction of polyethyleneimine with 2,4-tolylenediisocyanate. Silica gel and polysulfone bead-carriers coated with this polymer are used to remove heavy metal ions such as lead, cadmium, and mercury by adsorption. The polymer used is cross-linked and is insoluble in water.
I. Kiyota et al. in Japanese Kokai Patent No. JP 52/78291 (77/17291) [See Chemical Abstracts, Vol. 87, No. 22, 168863d] describe a number of complex polymer membranes. The polymer, including vinylpyridine, dimethylaminomethylstyrene, and dimethylaminomethylacrylate copolymer with unsaturated acids are quaternized with vinyl bromoacetate, alkyl halide, or p-chloromethylstyrene, complexed with polyamino compounds cast into fibers and cross-linked to produce membranes.
A. Stoy in U.S. Pat. No. 3,953,545 discloses polymers or copolymers (having nitrile side groups and strong acidic groups are contacted with silver or copper ions or their mixtures to produce silver and/or copper-containing polymers) useful as dialysis or filtration membranes, light-sensitive layers, catalysts, coatings, and the like.
In U.S. Pat. No. 4,254,087, R. R. Grinstead discloses a medium for the selective extraction of metal from aqueous acid solutions, such as leach liquors. The medium comprised (a) an alkylaromatic sulfonic acid with a molecular weight of at least 400, (b) a chelating amine having a pKa value for the amine group of 3-9 and having at least two coordinating centers in the molecule where at least one center is a ring nitrogen, and (c) a water-immisible diluent for (a) and (b). The extractants are especially useful for the selective extraction of nickel, cobalt, or copper from aqueous acid and leach liquors containing another metal.
In U.S. Pat. No. 4,356,309, J. W. Falk et al. disclose the use of an N-alkylated-2-(2-pyridyl)imidazole compound as a selective extractant for cobalt, copper, and nickel from aqueous solutions.
Japanese Patent No. 60118288, a patent assigned to NEC Corporation discloses a process for the removal of iron and calcium and other metal ions such as nickel, zinc, copper, cadmium, lead, cobalt, and the like using a complexing agent such as amino carboxylic acid, nitrilotriacetic acid, hydroxycarboxylic acid, citric acid, tartaric acid, etc.) The metal complex is insoluble and is precipitated from solution.
The above references do not disclose a process for the removal of metal ions from aqueous solutions as is described in the present invention. It is extremely useful to have a single-phase reaction to remove metals from aqueous solution which is faster than existing systems.